The Schottky barriers of Ti, Mo, Co, Ni, Pd, and Au on (100) β-Ga2O3 substrates were analyzed using a combination of current-voltage (J-V), capacitance-voltage (C-V), and current-voltage-temperature (J-V-T) measurements. Near-ideal, average ideality factors for Ti, Mo, Co, and Ni were 1.05–1.15, whereas higher ideality factors (∼1.3) were observed for Pd and Au contacts. Barrier heights ranging from 0.60 to 1.20 eV were calculated from J-V measurements for the metals with low ideality factors. C-V measurements of all Schottky metals were conducted and yielded average barrier heights ranging from 0.78 to 1.98 eV. J-V-T measurements of Ti and Co diodes yielded barrier heights of 0.81 and 1.35 eV, respectively. The results reveal a strong positive correlation between the calculated Schottky barrier heights and the metal work functions: the index of interface behavior, S = 0.70, 0.97, and 0.81 for J-V, C-V, and J-V-T data, respectively.

In this study, electrical properties of four metals (W, Mo, Au, Ni) as Schottky contacts on n-type (100)-oriented β-Ga2O3 substrates grown by the Czochralski method are reported. The Schottky barrier heights for each metal contact were calculated from I-V and/or C-V measurements. Two methods were used to cross check the Schottky barrier heights (φB) and ideality factors (n) calculated from I-V measurements. The Schottky barrier height values calculated from C-V and I-V measurements showed excellent agreement with each other and increased with an increase in the metal work functions. Some anomalous behavior of Au contacts, which is similar to behavior reported on (010)-oriented β-Ga2O3, is also described.

Phase and microstructural evolution of gallium oxide (Ga2O3) films grown on vicinal (0001) sapphire substrates was investigated using a suite of analytical tools. High-resolution transmission electron microscopy and scanning transmission electron microscopy of a film grown at 530 °C revealed the initial pseudomorphic growth of three to four monolayers of α-Ga2O3, a 20–60 nm transition layer that contained both β- and γ-Ga2O3, and a top ∼700 nm-thick layer of phase-pure κ-Ga2O3. Explanations for the occurrence of these phases and their sequence of formation are presented. Additional growths of Ga2O3 films in tandem with x-ray diffraction and scanning electron microscopy investigations revealed that the top layer varied in phase composition between ∼100% κ-Ga2O3 and ∼100% β-Ga2O3; the surface microstructure ranged from poorly coalesced to completely coalesced grains as a function of growth temperature, growth rate, or diluent gas flow rate. In general, it was found that the κ-phase is favored at lower growth temperatures and higher triethylgallium flow rates (low VI/III ratios). The growth of nominally single-phase κ-Ga2O3 within the top layer was observed in a temperature range between 500 and 530 °C. Below 470 °C, only amorphous Ga2O3 was obtained; above 570 °C, only the β-phase was deposited.

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Ga2O3 films were deposited on (100) MgAl2O4 spinel substrates at 550, 650, 750, and 850 °C using metal-organic chemical vapor deposition and investigated using x-ray diffraction and transmission electron microscopy. A phase-pure γ-Ga2O3-based material having an inverse spinel structure was formed at 850 °C; a mixture of the γ-phase and β-Ga2O3 was detected in films grown at 750 °C. Only β-Ga2O3 was determined in the films deposited at 650 and 550 °C. A β- to γ-phase transition occurred from the substrate/film interface during growth at 750 °C. The growth and stabilization of the γ-phase at the outset of film growth at 850 °C was affected by the substantial Mg and Al chemical interdiffusion from the MgAl2O4 substrate observed in the energy-dispersive x-ray spectrum. Atomic-scale investigations via scanning transmission electron microscopy of the films grown at 750 and 850 °C revealed a strong tetrahedral site preference for Ga and an octahedral site preference for Mg and Al. It is postulated that the occupation of these atoms in these particular sites drives the β-Ga2O3 to γ-phase transition and markedly enhances the thermal stability of the latter phase at elevated temperatures.

This has motivated attempts to develop photocatalysts with enhanced charge-separation properties using defect engineering, [5,6] facet engineering, [7][8][9] and the construction of heterojunctions. [10][11][12] Recently, molten salt treatments have been used for synthesis and to optimize photocatalyst properties. [13,14] In a molten salt, the mass transfer between precursors is accelerated and, compared with conventional solid-state synthesis, lower reaction temperatures can be used. [15,16]